Komatsu PC120LC-6 Fault Code E208: Meaning and Fix

What is Komatsu PC120LC-6 Fault Code E208?

Fault Code E208 on the Komatsu PC120LC-6 indicates a malfunction in the engine speed sensor circuit, specifically detecting an abnormal or missing signal from the engine RPM sensor.

This fault is triggered when the Engine Control Module (ECM) fails to receive a valid pulse signal from the magnetic pickup sensor mounted on the flywheel housing. The engine speed sensor is critical for fuel injection timing, governor control, and overall engine management on the Komatsu 6D95L engine powering this excavator.

Without accurate RPM data, the ECM cannot properly regulate fuel delivery, resulting in poor performance or complete engine shutdown as a protective measure.

Common Symptoms

• Engine fails to start or cranks but won't fire
• Erratic engine RPM fluctuations during operation
• Sudden engine shutdown without warning
• Monitor panel warning light illuminates with E208 displayed
• Loss of auto-idle function and throttle response issues

Potential Causes

The most frequent causes of E208 on used PC120LC-6 units include:

• Damaged or worn engine speed sensor (common on machines with 8,000+ hours)
• Corroded or loose connector pins at the sensor harness junction
• Chafed wiring harness where it routes near the flywheel housing or exhaust manifold
• Excessive flywheel ring gear wear causing inconsistent sensor gap
• ECM internal circuit failure (less common but possible on older units)
• Contaminated sensor tip from oil or metallic debris

How to Troubleshoot and Fix Code E208

Step 1: Visual Inspection Locate the engine speed sensor on the left side of the flywheel housing. Inspect the wiring harness for abrasion, heat damage, or rodent chewing—particularly where it passes near hot exhaust components. On used excavators, check connectors for green corrosion or stretched pins.

Step 2: Electrical Testing Using a digital multimeter, measure sensor resistance between terminals. The specification is typically 190-250 ohms at room temperature. Test continuity from the sensor connector to the ECM pins to identify open circuits. Verify 12V reference voltage is present at the connector with the key on.

Step 3: Sensor Gap and Signal Verification Confirm the air gap between the sensor tip and flywheel teeth is within 0.5-1.5mm. While cranking, use an oscilloscope or AC voltage function to verify the sensor generates a pulsing signal (minimum 1.0V AC).

Step 4: Component Replacement If testing confirms sensor failure, replace with an OEM-equivalent magnetic pickup sensor. Always clean the mounting surface and apply anti-seize to threads.

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Disclaimer: This guide provides general technical information. Always consult Komatsu service documentation and qualified heavy equipment technicians for diagnosis and repairs.